Since fiber-reinforced composite material made of reinforcing fibers and a matrix resin is lightweight and has excellent mechanical characteristics, it is used in a wide variety of applications, for example, structural material such as that in aircraft, vehicle bodies, ships and buildings, along with sporting goods such as golf shafts, fishing rods and tennis rackets.
Various methods are available for manufacturing fiber-reinforced composite material. Among them, a widely employed method is to use a sheet-, tape- or string-shaped prepreg, which is an intermediate made by impregnating a matrix resin composition into a reinforcing fiber material. A molded article is obtained by laminating multiple prepregs and by applying heat on the prepreg laminate.
As a matrix resin composition for forming a prepreg, either thermosetting or thermoplastic resins may be used, but thermosetting resin is used more often.
When fiber-reinforced composite material is manufactured by using a prepreg, the amount of resin flow is often the issue. Namely, if the viscosity of a matrix resin composition is lowered so that the matrix resin composition is sufficiently impregnated into a reinforcing fiber material, a significant amount of the matrix resin composition may flow out when the obtained prepreg is thermally compressed during a molding process. Accordingly, problems may arise such as poor appearance of the molded article and meandering reinforcing fibers that in turn cause reduced physical properties. By contrast, if the viscosity of a matrix resin composition is increased so that the amount of resin flow is appropriately controlled, such a viscosity level tends to cause a decrease in the results of impregnation into the reinforcing fiber material and the drapability of the resultant prepreg.
Patent Literature 1 proposes a composition for heat-compression molding; the composition is formed using a core-shell type copolymer so as to increase its viscosity by applying heat.